MXene/Au photocatalytic nitrogen fixation material, and preparation method and application thereof
Technical Field
The invention belongs to the field of photocatalytic materials, and particularly relates to an MXene/Au photocatalytic nitrogen fixation material, and a preparation method and application thereof.
Background
Energy is the most basic driving force for sustainable development of human society and also an important material basis on which human beings live. The traditional fossil fuel still occupies the leading position of the current energy supply and demand system, however, with the increasing exhaustion of fossil energy, the sustainable development of the world economy is severely restricted, and the energy problem becomes one of the main problems facing human beings at present. The vigorous development of green and renewable new energy sources becomes a primary task of research of all countries in the world. As a typical green renewable clean energy source, ammonia is not only a vital chemical raw material used for manufacturing chemical fertilizers, explosives, medicines, plastics and other industries, but also an important energy storage intermediate and a carbon-free energy carrier. More importantly, the ammonia provides a brand-new energy market, is not limited by regional distribution, and brings unique market advantages and opportunities for the ammonia. Therefore, the ammonia becomes one of the leading research directions in the field of green sustainable fresh energy, a series of potential problems caused by market centralization due to regional factors and the market centralization are solved, the ammonia is expected to be the most promising green clean energy, and the sustainable dependence on fossil fuel transition in the rapid development of economy in the world is relieved.
Currently, industrial NH 3 The production still adopts the traditional Haber-Bosch process technology, which takes iron or ruthenium-based material as catalyst and uses high-purity N 2 And H 2 The gas flow is realized under the conditions of high temperature (300 ℃ C. and 550 ℃ C.) and high pressure (20-30 MPa). The NH 3 The production process is a high-energy-consumption process, the preparation conditions are harsh, the requirements on production equipment are high, and the production process still dominates the current industrial ammonia synthesis industry. Therefore, the method explores and realizes the high-efficiency reaction of nitrogen and water at normal temperature and normal pressure to synthesize ammonia, simultaneously utilizes sustainable green clean energy as the supply of driving energy in the ammonia synthesis process, can thoroughly overcome the problems of high energy consumption, high carbon emission, safety and the like in the traditional Haber-Bosch method ammonia synthesis process technology, has important practical research significance for relieving the energy crisis and meeting the increasing ammonia demand, and can bring huge revolution and economic benefits to the sustainable development of human society and economy, human production and life style. The photocatalytic nitrogen fixation utilizes solar energy as energy driving force, realizes zero emission of carbon in chemical industrial production in real sense, and is a clean, green, sustainable, high-efficiency and high-selectivity ammonia synthesis process technology.
The design and construction of the photocatalyst material are the leading and core of the photocatalytic ammonia synthesis technology. Compared with the traditional block nanometer material, the two-dimensional semiconductor nanometer sheet can effectively improve the electron mobility and the surface energy, thereby ensuring the effective light absorption utilization rate and the adsorption to the target reactant and further promoting the interface catalysisThe reaction is generated, and photo-generated electrons are rapidly transferred from the interior of the material to the surface, so that high separation efficiency of bulk charges is ensured. Thus, two-dimensional semiconductor nanosheets exhibit unique advantages that are not replaceable in photocatalytic applications. MXene as a novel two-dimensional layered material has excellent physical properties and chemical properties, particularly abundant terminal groups easy to regulate and control on the surface, a unique morphological structure, excellent optical absorption performance, adjustable forbidden band width and excellent electron transmission efficiency, so that the MXene material has unique optical, electrical, magnetic and thermal properties, and is expected to be a promising photocatalyst material in view of the unique properties of the MXene material. Theoretical analysis shows that the existence of surface-O terminal group can greatly limit MXene material surface to N 2 The adsorption capacity of the nitrogen-fixing catalyst is further influenced, and the photocatalytic nitrogen-fixing performance of the nitrogen-fixing catalyst is further influenced. In addition, the photocatalytic performance of the MXene material is limited by the problems of interlayer stacking, complex surface modification functional group, limited number of photon-generated carriers and the like, and the photocatalytic nitrogen fixation performance is severely limited.
The plasmon Au nano-particles have excellent optical properties, can excite the local surface plasmon resonance thereof through photon absorption, and are widely applied to the fields of optical sensing, biomedicine, solar cells, light, electro-catalysis and the like. The plasmon Au nano-particles have a plurality of advantages, including (1) the resonance wavelength can be adjusted in a system from ultraviolet to infrared light region, and the light capture capability is enhanced; (2) high-energy hot carriers are generated to drive chemical reaction; (3) photothermal effect and the like, which are caused by converting light into heat in the process of carrier attenuation, have been widely used to drive photochemical reactions or enhance the photocatalytic performance of catalysts. The MXene/Au composite material of the interlayer is constructed based on a plurality of optical advantages of Au local surface plasmon resonance, the limitations of MXene interlayer self-stacking, low interlayer active site utilization rate and the like can be solved, and the MXene material photocatalysis nitrogen fixation effect is improved by utilizing the Au plasmon resonance effect.
Disclosure of Invention
The object of the present invention is to construct Ti 3 C 2 MXene composite photocatalyst and preparation of different sizesAnd embedding it in Ti 3 C 2 Interlaminar, not only can solve Ti 3 C 2 The interlayer stacking problem of the material per se is solved, the utilization rate of the interlayer active sites is improved, and meanwhile, the local surface plasmon effect of the Au nanospheres is utilized to improve the layered Ti 3 C 2 The material has the photocatalysis nitrogen fixation effect.
The invention also provides layered Ti 3 C 2 The preparation method comprises the following steps of preparing a material, a layered MXene material with a partially Ti-reduced surface, preparing MXene/Au composite materials with different Au sizes and different Au attachment positions, and applying the MXene/Au composite materials to photocatalysis and nitrogen fixation.
In order to realize the purpose, the invention adopts the technical scheme that:
a preparation method of an MXene/Au photocatalytic nitrogen fixation material comprises the following steps:
(1) preparation of layered Ti 3 C 2 Materials for standby;
(2) preparation of surface locally reduced Ti layered Ti 3 C 2 Materials: weighing layered Ti 3 C 2 A material containing 5-10% by volume of N in hydrogen 2 /H 2 Annealing for 5-7 h at 180-220 ℃ in mixed atmosphere to obtain layered Ti with local Ti reduction on the surface 3 C 2 Material, denoted r-Ti 3 C 2 ;
(3) Form a layer of Ti 3 C 2 Or r-Ti 3 C 2 Ultrasonically and uniformly dispersing the material in water, then adding an Au ball solution coated with sodium citrate or a gold ball solution coated with CTAB, ultrasonically and uniformly dispersing, rotatably evaporating out a solvent, and drying to obtain the titanium-doped titanium dioxide (Ti) with 0.1g of layered Ti per layer 3 C 2 Or r-Ti 3 C 2 The material required 10mL of water and 5mL of sodium citrate coated Au ball solution or CTAB coated gold ball solution.
Further, the sodium citrate coated gold ball was prepared as follows: 50mL of chloroauric acid solution with the concentration of 0.01wt% is stirred and heated to boiling; and respectively adding 2-4.5 mL of 1wt% sodium citrate solution into the boiling chloroauric acid solution, and stirring and reacting for 20-40 min to obtain sodium citrate-coated gold ball solutions with different sizes.
Further, the addition amounts of the 1wt% sodium citrate solutions were 4.5mL, 3mL, and 2mL, respectively, to obtain sodium citrate-coated gold ball solutions with sizes of 13nm, 16nm, and 20nm, respectively.
Further, the CTAB coated gold ball was prepared as follows:
(1) preparing a seed solution: 0.25 mL of 0.01M HAuCl 4 The solution was added to 9.75 mL of 0.1M CTAB solution and mixed well, then 0.60 mL of fresh 0.01M NaBH was added 4 Shaking the solution evenly, and standing for 2-4 h at room temperature;
(2) 0.12 mL of the seed solution was added to 9.75 mL of a 0.1M CTAB solution, 190 mL of ultrapure water, 4 mL of 0.01M HAuCl 4 And 15 mL of ascorbic acid with the concentration of 0.1M, shaking uniformly, and keeping the temperature for 8-12 hours.
Further, in the step (2), N 2 /H 2 The volume ratio of hydrogen in the mixed gas is 5%, the annealing temperature is 200 ℃, the treatment time is 6h, and the gas flow is 50 mL/min.
Further, the rotating speed during rotary steaming is 80 r/min, the pressure is 0.1MPa, and the heating temperature of the rotary steaming bottle is 50 ℃.
Further, in the step (3), the power for ultrasonic dispersion was 100W, and drying was performed at 60 ℃.
The MXene/Au photocatalysis nitrogen fixation material prepared by the preparation method.
The MXene/Au photocatalytic nitrogen fixation material is applied to photocatalytic nitrogen fixation.
More preferably, the specific process of photocatalytic nitrogen fixation is as follows: weighing 80mg of photocatalytic nitrogen fixation material, putting the photocatalytic nitrogen fixation material into a photocatalytic reactor, adding 50mL of pure water, ultrasonically dispersing the mixture uniformly, and then continuously introducing N into the reactor at the flow rate of 100mL/min 2 And (3) about 20 min-40 min, then, starting a 300W xenon lamp light source to irradiate the reaction liquid in the photocatalytic reactor from the upper part, adjusting the nitrogen flow to be 50mL/min, taking 2mL of reaction liquid every 1 hour, centrifugally separating out the catalyst, and detecting and calculating the ammonia yield by using a Nashin reagent color development method.
The invention combines the technical means of rotary evaporation and the solvent dynamic driving methodAnd the surface charge repulsion/adsorption principle to construct the layered Ti of the interlayer Au ball intercalation 3 C 2 The Au/Au composite material finally improves the photocatalytic nitrogen fixation efficiency of the composite material by virtue of the local surface plasmon resonance effect of the Au ball. The method is also suitable for constructing composite materials with sandwich structures of other layered materials and metal particles.
Drawings
FIG. 1 is Ti 3 C 2 ,r-Ti 3 C 2 ,Ti 3 C 2 /Au,r-Ti 3 C 2 XRD pattern of Au material;
FIG. 2 is Ti 3 C 2 ,r-Ti 3 C 2 A map of Ti2p of the material;
FIG. 3 is Ti 3 C 2 ,r-Ti 3 C 2 Scanning electron microscope images of materials, wherein (a) Ti 3 C 2 ,(b)r-Ti 3 C 2 ;
FIG. 4 is a scanning electron micrograph of Au spheres of different sizes and their particle size distribution, (a) 13nm sodium citrate coated Au; (b) 16nm sodium citrate coated Au; (c) 20nm sodium citrate coated Au; (d) 20nm CTAB coated Au;
FIG. 5 is a sandwich structure of Ti 3 C 2 /Au,r-Ti 3 C 2 Scanning electron microscope image of Au material, (a) Ti 3 C 2 /Au,(b)r-Ti 3 C 2 /Au;
FIG. 6 shows Ti attached to the edges of the layers 3 C 2 /Au,r-Ti 3 C 2 Scanning electron microscope image of Au material, (a) Ti 3 C 2 /Au,(b)r-Ti 3 C 2 /Au;
FIG. 7 is Ti 3 C 2 ,r-Ti 3 C 2 ,Ti 3 C 2 /Au,r-Ti 3 C 2 A photocatalytic nitrogen fixation performance diagram of an Au material; (a) ammonia production of different catalyst materials under full spectrum; (b) ammonia production of different catalyst materials under visible light; (c) comparing the ammonia production rates of different catalysts;
FIG. 8 is a comparison of the photocatalytic nitrogen fixation performance of the composite material at different Au attachment sites.
Detailed Description
Technical objects, technical solutions and effects of the present invention will be further described in order to make the technical objects, technical solutions and effects of the present invention clearer, but the examples are intended to explain the present invention and should not be construed as limiting the present invention, and those who do not specify a specific technique or condition in the examples are performed according to the techniques or conditions described in the literature in the art or according to the product specification.
Example 1
Ti with sandwich structure 3 C 2 The preparation method of the Au composite material comprises the following steps:
(1) layered Ti 3 C 2 Preparation of the material: weighing 2g of Ti 3 AlC 2 Adding the ceramic phase precursor into 20 mL of 40% HF solution, stirring and etching at 35 ℃ for 48h, centrifuging to obtain powder, repeatedly washing with high-purity water to neutrality, and drying the obtained powder in a vacuum oven at 60 ℃ to obtain layered Ti 3 C 2 A material.
(2) Surface local Ti reduced layered Ti 3 C 2 Preparation of the material: 0.5g of the layered Ti thus obtained was weighed 3 C 2 Material of 5% by volume N in hydrogen 2 /H 2 Annealing for 6 hours at 200 ℃ in mixed atmosphere with gas flow of 50mL/min to obtain the lamellar Ti with local Ti reduction on the surface 3 C 2 Material (r-Ti for short) 3 C 2 )。Ti 3 C 2 ,r-Ti 3 C 2 The map of the Ti2p of the material is detailed in fig. 2. The main objective of XPS profiling was to evaluate Ti 3 C 2 ,r-Ti 3 C 2 The valence state of Ti on the surface of the material exists and the relative content is large. As can be seen from FIG. 2, Ti 2+ , Ti 3+ , Ti 4+ The relative intensity of the component contents can clearly vary between Ti and Ti 3 C 2 ,r-Ti 3 C 2 Observed in the material. After thermal reduction treatment, r-Ti 3 C 2 In the material Ti 2+ , Ti 3+ The strength of the component is obviously enhanced, and Ti 4+ The strength of the component content is obviously reduced, which indicates that Ti 3 C 2 Ti on the surface of the material 4+ The component is partially reduced to Ti with low valence state by thermal reduction treatment 2+ , Ti 3+ And (4) components.
Ti 3 C 2 ,r-Ti 3 C 2 The scanning electron micrograph of the material is shown in detail in FIG. 3. As can be seen from FIG. 3, Ti was produced 3 C 2 ,r-Ti 3 C 2 The materials are all of multilayer laminated structures, and the original laminated structures cannot be damaged in the thermal reduction treatment process.
(3) Sandwich structure of Ti 3 C 2 Preparation of Au composite: first, 0.1g of Ti was weighed 3 C 2 The material is prepared by uniformly dispersing the material in 10mL of high-purity water by ultrasonic wave (100W), adding 5mL of Au ball solution coated with sodium citrate with certain particle concentration and different sizes, uniformly dispersing the Au ball solution by ultrasonic wave of 100W for 10min, and by means of a rotary evaporation technical means, the rotating speed is 80 r/min, the pressure is 0.1MPa, the heating temperature of a water bath on a rotary evaporation bottle is 50 ℃, the Au ball solution is continuously evaporated by a hydrosolvent, and meanwhile, the surface of a gold ball coated with the sodium citrate is negatively charged, and Ti is coated on the surface of the gold ball 3 C 2 The edges of the layers are also negatively charged and there is electrostatic repulsion. Therefore, under the synergistic effect of the dynamic driving effect and the electrostatic repulsion effect of the water solvent in the rotary evaporation process, the Au spherical particles are gradually driven to the layered Ti 3 C 2 Between the layers of (2) to construct a sandwich structure of Ti 3 C 2 And placing the Au composite material in a vacuum oven at 60 ℃ for drying to obtain the composite material.
(4) r-Ti with sandwich structure 3 C 2 Preparation of Au composite: mixing Ti 3 C 2 The material was changed to 0.1g of r-Ti 3 C 2 And the other steps are the same as the step (3).
The preparation process of the sodium citrate coated gold ball is as follows:
50mL of a 0.01wt% chloroauric acid solution was heated with stirring to boiling (about 150 ℃ C.); and respectively adding 4.5mL, 3mL and 2mL of 1wt% sodium citrate solution into the boiling chloroauric acid solution, and stirring and reacting for 30min to obtain the 13nm, 16nm and 20nm sodium citrate-coated Au balls. Scanning electron micrographs of Au spheres of different sizes and particle size distribution maps thereof are detailed in FIGS. 4 (a-c), wherein (a) Au is coated with 13nm sodium citrate; (b) 16nm sodium citrate coated Au; (c) 20nm sodium citrate coated Au.
FIG. 1 is Ti 3 C 2 ,r-Ti 3 C 2 ,Ti 3 C 2 /Au,r-Ti 3 C 2 XRD analysis of Au material, as can be seen from FIG. 1 (a), after HF acid etching, at 2 θ =8.9, 18.4 and 27.5 o The diffraction peaks at the positions correspond to (002), (004) and (008) crystal faces and originally belong to Ti 3 AlC 2 The diffraction peak of the crystal face is obviously reduced or disappears, which shows that Ti 3 AlC 2 Reacts with HF acid, the original structure is damaged, the Al layer is etched and stripped, and the layered Ti is successfully prepared 3 C 2 A material. As shown in FIG. 1 (b), with Ti 3 C 2 Compared with the material, the r-Ti after thermal reduction treatment 3 C 2 The material is 23.3 o And a new diffraction peak appears at the position, which corresponds to a (006) crystal face, and the interlayer spacing is enlarged after the thermal reduction treatment, so that the interlayer structure is more excellent. As can be seen from FIG. 1 (c), after being compounded with Au spherical nanoparticles, the characteristic diffraction peak of cubic phase Au is clearly shown in Ti 3 C 2 /Au,r-Ti 3 C 2 In the XRD spectrum of the/Au composite material, the successful combination of the Au ball particles is shown.
FIG. 5 is Ti from Au coated with 13nm sodium citrate 3 C 2 /Au,r-Ti 3 C 2 Scanning electron microscope image of Au material. As can be seen from FIG. 5, Ti was obtained 3 C 2 /Au,r-Ti 3 C 2 The Au material presents a clear sandwich structure, and Au nanospheres are uniformly embedded in Ti 3 C 2 ,r-Ti 3 C 2 Between layers of material.
Example 2
Ti with attached layer edge 3 C 2 /Au,r-Ti 3 C 2 The preparation method of the Au composite material comprises the following steps:
the same procedure as in example 1 was repeated except that 5mL of cetyltrimethylammonium bromide (CTAB) -coated Au beads were used instead of the Au bead solution coated with sodium citrate.
The preparation process of the CTAB coated gold ball is as follows:
preparing a seed solution: HAuCl 4 The solution (0.01M, 0.25 mL) was added to the CTAB solution (0.1M, 9.75 mL) and mixed well, followed by the rapid addition of fresh NaBH 4 The solution (0.01M, 0.60 mL) was shaken well and allowed to stand at room temperature for 3 h.
0.12 mL of the seed solution was added to CTAB (0.1M, 9.75 mL), ultrapure water (190 mL), HAuCl 4 After shaking in a mixture of (0.01M, 4 mL) and ascorbic acid (0.1M, 15 mL), the mixture was left at room temperature for 10 hours, and its SEM image and particle size distribution chart are shown in FIG. 4d, from which FIG. 4d, it is seen that 20nm CTAB-coated Au was obtained.
FIG. 6 shows Ti attached to the edges of the layers 3 C 2 /Au,r-Ti 3 C 2 Scanning electron microscope image of Au material. As shown in the figure, Au nanospheres are uniformly attached to Ti 3 C 2 ,r-Ti 3 C 2 Ply-edge position of the material.
Photocatalytic nitrogen fixation test
The photocatalytic nitrogen fixation reaction test was specifically carried out at room temperature in a sealed quartz photocatalytic reactor having a diameter of 6cm and a volume of 100 mL. The specific experimental process is as follows: 80mg of catalyst is weighed and placed in a photocatalytic reactor, 50mL of pure water is added, and ultrasonic dispersion is carried out for 5 minutes to ensure that the catalyst powder is uniformly dispersed. Then, at 100mL min -1 Flow of (2) into the reactor continuously 2 About 30min, at which time the reactor was in a gas continuous cycle. Subsequently, a 300W xenon lamp light source was turned on to irradiate the reaction liquid in the photocatalytic reactor from above, and the nitrogen flow rate was adjusted to 50 mL/min. Every 1 hour, 2mL of reaction solution is taken for centrifugal separation of the catalyst, and the ammonia yield is detected and calculated by a Naeseler reagent color development method.
FIG. 7 is Ti 3 C 2 ,r-Ti 3 C 2 ,Ti 3 C 2 /Au,r-Ti 3 C 2 Au (Ti made of Au coated with 13nm sodium citrate) 3 C 2 /Au,r-Ti 3 C 2 Au) material photocatalysis nitrogen fixation performance diagram. As can be seen from FIG. 7, Ti 3 C 2 The material has almost no photocatalysis nitrogen fixation effect, and after thermal reduction treatment, the r-Ti 3 C 2 The photocatalytic nitrogen fixation performance is improved, and the ammonia production rate is 1.25 mu mol/h/g under white light cat. Showing that r-Ti was reduced 3 C 2 The material exhibits more effective active sites. After complexing with Au balls, Ti 3 C 2 Au has ammonia generating rate of 1.91 mu mol/h/g under white light cat. The improvement of the photocatalytic nitrogen fixation effect is mainly due to the thermal electron effect of the Au ball. However, r-Ti 3 C 2 The photocatalytic nitrogen fixation efficiency of Au material is obviously improved, and the ammonia production rate reaches 22.6 mu mol/h/g cat. The method proves that the local surface plasmon effect of Au is beneficial to improving the light energy utilization rate, more effective high-energy hot carriers are brought, and the photocatalytic nitrogen fixation efficiency of the composite material is further improved.
FIG. 8 shows the sandwich structure of 20nm sandwich made of r-Ti prepared in example 1 3 C 2 Au and the 20nm layer prepared in example 2 with r-Ti attached to the sides 3 C 2 And the photocatalysis nitrogen fixation performance of the Au composite material is compared. The results show that the r-Ti is attached to the layer edge position with the same Au size and the same Au loading amount 3 C 2 The ammonia production rate of the/Au @ CTAB is 16.63 mu mol/h/g cat. Significantly lower than the sandwich structure with interlaminar embedding 3 C 2 Ammonia production rate of 26.82 mu mol/h/g of/Au @ citrate cat. This indicates that the layer edge adhesion reduces the utilization of the interlayer active sites, resulting in a reduction in the photocatalytic nitrogen fixation performance.
Finally, in the invention, relevant parameters for constructing the composite material can be adjusted in corresponding ranges, and the size of the obvious Au ball, the composite concentration of the Au ball, the type of the MXene material and the like can be correspondingly replaced or modified. The above embodiments are merely intended to illustrate the technical solution of the present invention and not to limit the same, and although the present invention has been described with reference to preferred embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.